1. Field of the Invention
This invention relates to fuel rod inspection techniques for nuclear reactors, and the like and, more particularly, to a combination of fuel rod end cap, cellular end fitting and radiation sensing device probe for fuel rod integrity inspection, and the like.
2. Description of the Prior Art
Ordinarily to extract useful power from a nuclear reactor it is necessary to assemble a suitable concentration of fissionable material in the reactor core. This fissionable material usually is prepared as an oxide of uranium or plutonium, the oxide being pressed into pellets that are loaded into long, hollow tubes. These tubes, when capped and sealed, are called fuel rods. As a general matter, to reduce production costs, and the like, it is customary to use solid metal plugs that are welded in place within the fuel rod tube.
To enhance the strength of the array of fuel rods that comprise the reactor core, it has been the practice to subdivide these fuel rods into individual structural groups. Each of these groups is composed of about two hundred fuel rods that are bound together to form a fuel assembly which can be inserted into or withdrawn from the reactor core.
The fuel rods in each of these fuel assemblies are bound together in a number of ways. Typically, an array of cellular grids are positioned at various stations along the length of the fuel rods in the assembly. The dimensions of the individual cells, moreover, enable the metal plates that comprise the grids to engage the adjacent surfaces of the rods and thereby stabilize and sustain these fuel rods in proper core position. The ends of the fuel rods often are received in end fittings to add further mechanical support. Frequently, heavy and expensive castings in rather unique shapes are used as end fittings. Not only are these castings costly, but they are also difficult to manufacture.
These prior art cast end fittings also impose a further and more serious difficulty. This latter difficulty arises from the fact that the fuel rods in the reactor core must cope with an extremely hostile environment. Temperature, pressure, vibration and radiation effects, for example, all are extreme in the typical reactor core, and all tax the structural integrity of each of the fuel rods. Naturally, routine inspections of the fuel rods are mandatory in order to identify those rods that have developed leaks or otherwise failed in service.
Usually these inspections are accomplished by withdrawing a fuel assembly from the reactor core and placing the fuel assembly in a container. A fluid is pumped through the container and the radiation level of the fluid that is discharged from the container is monitored. An unusually high level of radioactivity in the fluid that is discharging from the container is indicative of one or more leaking fuel rods in the assembly or, perhaps, "tramp" radioactive material that is being scoured from the rod surface by the fluid. In any event, if an unusually high level of radioactivity is observed, the fuel assembly then must be disassembled with the aid of remotely controlled manipulators. Subsequent to the foregoing disassembly, each of the fuel rods in the fuel assembly must be individually inspected to identify the leaking fuel rod or rods. The failed fuel rod or rods then are withdrawn for reprocessing or further treatment and the fuel assembly is reassembled, again with the use of remote, radiation shielded manipulators, with the partially used rods and additional new fuel rods, as the case may be.
This procedure is, of course, time consuming and expensive. Clearly, there is a major industrial need to develop improved techniques for inspecting nuclear reactor fuel rods.